bump WP tested-up-to 5.8 in readmes

[jeffpaul]

Co-Authored-By: BBerg10up 72762903+BBerg10up@users.noreply.github.com

Description of the Change

Update readme(s) to reflect plugin has been tested on WordPress 5.8

Alternate Designs

N/A

Benefits

N/A

Possible Drawbacks

N/A

Verification Process

@BBerg10up tested as follows:

Tested this against 5.8 and compared the functionality in 5.7.2. I didn't notice any discrepancies or issues. Everything seemed to work exactly as the read.me defined.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Resolves #49.

Changelog Entry

Tested against WordPress 5.8